1. Field of the Invention
The present invention generally relates to 3-dimensional seismic exploration for oil, for example. More particularly, the present invention relates to an apparatus and method for 3-dimensional seismic exploration, which is precisely carried out even in a small ship.
2. Description of the Related Art
Generally, marine seismic explorations are carried out by an exploration vessel sailing on the sea, with seismic sources and streamers having hydrophones located behind the vessel, while sending seismic waves into the geological structures in the seabed, and collecting and analyzing the reflected seismic waves, thereby surveying the geological structures.
For such seismic exploration, an ocean bottom cable type streamer disclosed in Korean Patent Application Publication No. 10-2012-0076952, a streamer having a wing, a protecting casing, a loss-prevention means, and a water level-maintaining means, which is disclosed in Korean Patent Application Publication No. 10-2013-0134822, a multi-wave seismic exploration apparatus disclosed in Korean Patent No. 10-1016014, and a technology for converting collected reflected seismic waves into an ODCE file, which is disclosed in Korean Patent No. 10-1230040, are employed.
Seismic exploration using such apparatuses may be divided into 2D or 3D exploration depending upon whether a single streamer or two or more streamers were used. While 2D exploration acquires data of a vertical cross-section of subsurface geological structures, 3D exploration acquires data of a 3-dimensionally imaged cubic area of subsurface geological structures. Since subsurface geological structures actually have a 3-dimensional structure, 3D exploration is advantageous relative to 2D exploration in surveying subsurface geological structures. For 3D exploration, however, generally two or more rows of streamers are needed, so 3D exploration can only be done by a very large vessel.
In 3D seismic exploration using very large vessels such as an oil-exploration ship, the vessel moves over the sea with generally two or more rows of streamers launched, each of which extends a few kilometers or more, so, even when the streamers meet tidal current, they can be checked in their linearity and relative positions by means of several GPSs, due to their tension.
However, in the case of 3D seismic exploration using a small ship, if relatively short streamers of about 10 m, but not relatively long streamers of about 100 m, are used for the acquisition of 3D exploration data, the short streamers have little tension, so, if in a tidal current, they cannot be maintained at regular relative-positions.
FIGS. 1A and 1B show a conventional example of a 3D seismic exploration apparatus using a small ship. As shown in FIG. 1A, the 3D seismic exploration apparatus tows several 8m-streamers at a distance of 2 m, so as to acquire 3D seismic exploration data.
FIG. 1B shows two photographs, wherein an upper photograph illustrates seismic exploration in a river and a lower photograph illustrates seismic exploration at sea. As shown in the two photographs of FIG. 1B, in the sea region with a tidal current, the distance between the streamers is not constant as shown with the arrow, thus failing to obtain a precise 3D seismic image.
Further, compared to very large vessel sailing at about 5 knots for seismic exploration, a small ship sails at about 3 to 4 knots for seismic exploration. However, depending on the exploration direction, the water speed may often be less than 2 knots, making it difficult to maintain a constant distance between the streamers.
Accordingly, such problems should be overcome in order to facilitate 3D seismic exploration using a small ship.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.
Documents of Related Art
(Patent Document 1) Korean Patent Application Publication No. 10-2012-0076952
(Patent Document 2) Korean Patent Application Publication No. 10-2013-0134822
(Patent Document 3) Korean Patent No. 10-1016014
(Patent Document 4) Korean Patent No. 10-1230040